PP1513 - Clinical Assessment of the Vestibular Efferent System with oVEMP and Contralateral White Noise Suppression

Abstract:
The ocular vestibular evoked myogenic potential (oVEMP) measures utricular and superior vestibular nerve activity when an intense auditory stimulus is presented to the ear. The function of the afferent oVEMP pathway is well established; however, efferent system effects are understudied. We investigated how adding contralateral white noise to a standard recording protocol affects the oVEMP. Results indicated amplitude decreased incrementally as white noise intensity increased, suggesting successful activation of the efferent pathway and suppression of the response.

Summary::
Since its discovery, researchers and clinicians have strived to understand the vestibular efferent system's (VES) purpose. Animal studies have indicated the VES is involved in the differentiation of active and passive movements, modulation of vestibular sensitivity, top-down modulation, and participation in vestibular plasticity, but how that translates to humans remains poorly understood.

The ocular Vestibular Myogenic Evoked Potentials oVEMP is a measurable electrophysiologic response of curricular and superior vestibular nerve involvement in the otolith-ocular reflex activated by sound, pressure, or touch.

Studies have largely focused on afferent pathway contributions to the oVEMP while efferent pathway effects remain understudied. As such, the current project examined how responses changed following the introduction of a contralateral white noise during recording. It was hypothesized that the overall response amplitude would decrease as the intensity of the white noise increased.

oVEMPs were collected on 32 individuals between the ages of 20-55>(Mean: 30.45, SD: 11.72) All participants underwent a full case history, standard audiometric evaluation, immittance, and oVEMP testing under four different conditions (without white noise). Two runs of each condition were collected to ensure replicability using the belly-tendon montage on Natus Biologic hardware. Amplitude, latencies, and asymmetries were examined for change.

Results indicated amplitudes of N10 and P15 decreased incrementally as masker intensity increased except for 60 dB vs. 65 dB, which showed a strong trend towards significance. Latencies of N10 and P15, as well as ipsilateral oVEMP response amplitude/latency, were not affected by the presence of the masker.

Findings suggest activation of the efferent vestibular pathway was successfully achieved using the current protocol. The amount of activation is highly dependent on overall white noise intensity. These findings will prove useful as the clinical relevance of the vestibular efferent system continues to be explored.